1. Field of the Invention
The invention relates to an operating system which can be embedded in communications equipment.
2. Background of the Related Art
Generally, an OS (Operating System) provides various high level functions so that various software operations may be managed and performed effectively. In addition, the OS performs services for user processes generated in respective application programs through a Kernel real-time multi-managing system which manages resources, such as a disk, a printer, a terminal, or communication equipment.
When a user process generates a system call requiring OS service while operating a user program, the Kernel in the OS accesses an address area where data can be exchanged with the user process, and the OS then executes read/write functions with the data in order to exchange the data with the user processes. However, before the process is performed, the OS verifies the user memory validity in order to ensure the stability of the system operation and to protect Kernel resources from user access errors. In other words, if a real page is already allocated in the address area accessed by the OS as user memory, the address area cannot be used as the user memory, thus the validity of the user memory should be verified before the OS begins to exchange data.
Related art computer systems have OS where the address areas of the Kernel and of the user are different from each other. However, the OS installed on communications equipment coexists with the user area in a parallel address area. Therefore, if the Kernel accesses the memory area of the user in this OS environment, the Kernel is able to directly access the memory area without changing the address area. In other words, the Kernel is able to access the memory area without changing MMU (Memory Management Unit) data.
FIG. 1 is a schematic diagram of a related art OS provided for a user process. The related art user process of FIG. 1 includes text, data, heap, and stack areas in the memory, and the user process performs a system call in order to receive Kernel service from the OS. If the called user process requires an OS function, the virtual address area of the user buffer is transmitted to the Kernel. At that time, a memory error in the user process may generate a fatal error in the Kernel. Therefore, in order to prevent such an error, the Kernel determines whether the address of the user buffer is valid.
As described above, in order to ensure system stability, the OS protects the resources of the Kernel from an access error via a user using memory protection process. Generally, the Kernel assumes that any user may make an error and provides memory protection service to each user. Therefore, the data area of each user (buffer) goes through the validity verifying process before being used in the Kernel. A first related art method for verifying the validity of memory areas consists of searching the memory management structure allocated to the user application by the OS. A second related art method of verifying memory validity consists of searching an MMU structure by changing a virtual address into a real address.
To verify memory validity by searching an allocated memory management structure, when the user application asks the OS for permission to use the memory, the OS stores and manages the information in the memory in a certain structure set as a virtual address. The structure stores a start address number and the size of the allocated memory, in addition to the real memory information, and therefore the validity of the allocated memory is determined by searching the structure.
The first related art memory validity verification method is suitable for cases where the number of searched structures is small because the allocation form of the memory is simple. However, in the case of a telecommunication system in which the allocation and termination of the memory happens frequently due to the nature of the telecommunication protocol, the first related art memory validity verification method is not suitable because the number of executed searches, where Log N:N designates the size of the entire structure, becomes larger.
The second related art memory validity verification method is divided into a software based search, and a hardware based search in which the MMU hardware performs all searching functions automatically. The software based search allows the real address searching to be freely constructed by the developer of the OS, but it may affect the OS functioning. The hardware based search can be done by either a table lookup search, a hashing search, or a segment search method.
For the hardware based search, the table lookup method of searching stores mapping information in a table form, which implements the memory mapping information. In addition, the table area which is mapped is searched successively. The hashing method of searching is a method by which the structure is searched by changing the address using a certain hash function. The searching speed of this method is the fastest. However, the hashing method is complex due to the hash function and the size of the bucket. The complexity is further increased due to the overhead in case the corresponding structure is not found in the first bucket, whereby a secondary bucket should be used to find the corresponding structure. Such complexity increases the time to complete a hash method search.
The segment method of searching is advantageous for certain types of searches because of the difficulties with mapping a plurality of memories. The segment method is performed similarly to the page method of searching in accordance with applied processors.
As described above, problems with the conventional methods for verifying memory validity are due to the functioning of the method being varied by the hardware structure implementing the search, and the complexity of the search algorithym reducing the verifying speed. In addition, when a fault or a conflict is generated by a memory error in the Kernel, the OS is unable to respond appropriately and crashes or locks-up.